A groundbreaking new study has found that women with no history of fibromyalgia are at greater risk of developing the chronic and debilitating musculoskeletal pain disorder if they suffer from sleep problems.

Sleep disorders and poor quality sleep have been associated with increased risk for other chronic illnesses such as cardiovascular disease in previous studies, but this is the first to look for any link with fibromyalgia.

Researchers from the Norwegian University of Science and Technology in Trondheim, Norway, report in the journal Arthritis & Rheumatism that fibromyalgia risk is five times higher in women older than age 45 years who report "often" or "always" having sleep problems compared with women who regularly enjoy a good night's sleep. The scientists say the risk is greater the worse the sleep problems are and that the association is stronger among middle-aged and older women than among younger women.

Besides chronic widespread pain, sleep disturbances and excessive fatigue are common symptoms experienced by people with fibromyalgia. However, it has been unclear whether problems with sleep precede the development of the condition or whether they are the result of the pain experienced once fibromyalgia has become established. Of course both may be true.

In an effort to establish whether sleep disturbances play a role in the development of fibromyalgia, the Norwegian researchers carried out a prospective study (known as the 'HUNT' study) involving 12,350 women living in Norway's Nord-Trondelag County. None of the women had chronic musculoskeletal pain at the start of the study. The study itself involved the women completing two questionnaires and having clinical examinations, the first between 1984 and 1986 and the second between 1995 and 1997.

The follow-up surveys between 1995 and 1997 revealed that 327 of the women had been given a diagnosis of fibromyalgia since their first survey and examination the previous decade.

In analyses that took account of other factors that might influence the women's risk of developing fibromyalgia including smoking, education, physical exercise, and body mass index, the scientists found that women aged 45 and older who had sleep difficulties "often" or "always" were 5.41 times more likely to develop the condition than those who slept well, while those under 45 were 2.98 times more likely.

Comparing the 3,949 women who reported sleep problems of any frequency with the 8,401 who had no sleep disturbances at all, the researchers again found an elevated risk in those with sleep problems, albeit smaller at 2.10 times greater.

What the results show is that sleep problems of any kind and frequency more than double a woman's risk of developing fibromyalgia, whicle the risk increases with severity and frequency of sleep disturbance and a woman's age.

The researchers said: "If this reflects a true causal association, the attributable fraction is 65%, i.e., among women with sleep problems about two-thirds of the incident cases of fibromyalgia are caused by sleep problems."

This study does not provide an indication of how problems with sleep might cause fibromyalgia but previous research has shown that if deep sleep (stage 4) is interfered with in healthy volunteers, they tend to experience widespread pain akin to that suffered by fibromyalgia patients. Stage 4 sleep is known to be disrupted in fibromyalgia. Just how the sleep disturbances and pain become chronic in fibromyalgia remains unclear.